Plating apparatus for detecting the conductivity between plating contacts on a substrate

ABSTRACT

The present invention provides a conductivity sensing device capable of detecting the conductivity (contact state) of the plurality of feeder contacts contacting the conductive area of the substrate, and a plating apparatus capable of forming a plating film of uniform thickness by supplying a uniform plating current through a plurality of feeder contacts.

TECHNICAL FIELD

The present invention relates to a plating apparatus for plating asubstrate such as a semiconductor wafer or the like, and particularly toa plating apparatus capable of forming a plating film of uniformthickness by uniformly conducting a current on the substrate.

BACKGROUND ART

FIG. 1 shows the general construction of this type of conventionalplating apparatus. As shown in the drawing, the plating apparatusincludes a plating bath 10 accommodating a plating solution Q, in whicha substrate 12 such as a semiconductor wafer or the like mounted on ajig 11 and an anode 13 are disposed oppositely. A power source 14applies a predetermined DC voltage between the jig 11 and anode 13thereby forming a plating film on the substrate 12 by supplying anelectric current via the plating solution Q.

A feeder section 16 is provided on the jig 11. The feeder section 16includes a plurality of feeder contacts 15 contacting the conductivearea on the surface of the substrate 12. The power source 14 iselectrically connected to the feeder contacts 15 thereby a platingcurrent flows through the anode 13, substrate 12, and feeder contacts15.

Therefore, if the feeder contacts 15 do not reliably contact theconductive film on the substrate 12, either the plating process cannotbe performed or the plating film formed on the substrate 12 will not beuniform. The conventional apparatus does not have a method or device forfacilitating confirmation of the contact state between the feedercontacts 15 and the conductive film on the substrate 12.

DISCLOSURE OF INVENTION

In view of the foregoing, it is an object of the present invention toprovide a plating apparatus capable of forming a plating film of uniformthickness by supplying a uniform plating current through a plurality offeeder contacts contacting the conductive area of the substrate. It isanother object of the present invention to provide a conductivitysensing device for detecting the conductivity (contact state) of theplurality of feeder contacts.

To solve the above mentioned subject matter, there is provided a methodfor confirming conductivity state between a plating jig having aplurality of conducting pins and a substrate to be plated having aconductive film, the substrate being mounted on the plating jig having aplurality of conducting pins such that the conducting pins contact theconductive film thereon, the method comprising: disposing the conductingpins of the plating jig being electrically separated independently witheach other; attaching an end of reverse-current blocking diode to wiringconnecting to the conducting pins, and connecting to the other ends ofthe reverse-current blocking diodes together to wiring connecting to aplating power source; and measuring an electrical resistance between thewiring so as to measure the electrical resistance between conductingpins of the plating jig.

According to another aspect of the present invention, the conductivitystate detector may comprise a contact resistance measuring device formeasuring contact resistance between the feeder contacts and theconductive area on the surface of the substrate and detects theconductivity state of the feeder contacts based on the contactresistance measured by the contact resistance measuring device.

According to another aspect of the present invention, the conductivitystate detector may comprise a current sensor for detecting currentflowing through each of the plurality of feeder contacts and detects theconductivity state of the feeder contacts based on the current detectedby the current sensor.

According to another aspect of the present invention, the platingapparatus may comprise a plating current detector for detecting aplating current flowing through the feeder contacts; and a platingcurrent controller for maintaining a uniform plating current flowingthrough the feeder contacts based on output from the plating currentdetector.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows the general construction of a plating apparatus accordingto the conventional technology;

FIG. 2 is a cross-sectional view showing an example construction of thefeeder section for a plating apparatus according to the presentinvention;

FIG. 3 is a perspective view as viewed from the bottom showing thepositioning of feeder contacts mounted on the feeder ring of the feedersection and separated by insulating members;

FIG. 4 shows an example circuit construction for implementing a methodto confirm conductivity between the jig and wafer according to a firstembodiment of the present invention;

FIG. 5 shows a variation of the circuit construction in FIG. 4;

FIG. 6 shows the general construction of a conductivity sensing devicefor a plating apparatus according to the second embodiment;

FIG. 7 shows an example circuit construction of the conductivity sensingdevice in FIG. 6;

FIG. 8 shows the structure of an equivalent circuit for resistancesbetween feeder contacts;

FIG. 9 shows an example of a basic circuit construction for measuringresistance values between feeder contacts;

FIG. 10 shows an equivalent circuit for the feeder section of FIG. 3showing resistance of wiring material and resistance between the feedercontacts;

FIG. 11 shows the wiring configuration for measuring contact resistanceat the feeder contacts and supplying current for plating;

FIG. 12 shows an example circuit construction for a contact resistancemeasuring device disposed at the feeder contacts; and

FIG. 13 shows an example circuit construction for a plating currentsupplying device of the plating apparatus.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 2 is a cross-sectional view showing an example construction for afeeder section of a jig 11 according to a preferred embodiment of thepresent invention. As shown in the drawing, the feeder section includesan annular frame 17, an annular packing 18 disposed along the inner sideof the frame 17, a feeder ring 19 disposed along the inner side of thepacking 18, and a plurality of feeder contacts 15 arranged atpredetermined intervals on the feeder ring 19. The ends of the feedercontacts 15 contact and are electrically connected to a conductive area(not shown) formed on the outer surface of a substrate 12. The ends ofthe packing 18 are configured to closely contact and apply pressure tothe surface of the substrate 12 in order to prevent plating solutionfrom entering inside the packing 18. Hence, the feeder contacts 15,feeder ring 19, and the like are not exposed to the plating solution.

FIG. 3 is a perspective view showing the state of the feeder contacts 15mounted on the feeder ring 19. As shown in the drawing, the feedercontacts 15 are mounted at predetermined intervals along the feeder ring19. A plurality of insulating members 20 (four in this example)electrically divide the feeder ring 19 into sections, such that onefeeder contact 15 is mounted on each section of the feeder ring 19. Thedrawing shows a perspective view of the feeder ring 19 and the feedercontacts 15 attached thereto as viewed from the bottom.

FIG. 4 shows an example circuit configuration for implementing themethod of confirming conductivity between the semiconductor wafer(substrate to be plated) and jig according to the first embodiment ofthe present invention. As shown in the drawing, conducting pins 2-1,2-2, 2-3, and 2-4 contact the conductive film of the substrate 12mounted on the jig (not shown). The conducting pins serve as the feedercontacts of the jig and are disposed at intervals of 90 degrees aroundthe substrate 12. Each of the conducting pins is mounted on the jig asshown in FIG. 3. One ends of wires 3-1, 3-2, 3-3, and 3-4, are connectedto the conducting pins 2-1, 2-2, 2-3, and 2-4, respectively. The otherends of the wires are connected to the negative electrode of the powersource 5.

A resistance measuring device 4-1 is connected between the wires 3-1 and3-3. A resistance measuring device 4-2 is connected between the wires3-2 and 3-4. A jig having the circuit configuration described above isdisposed opposite the anode 13 in the plating solution Q contained inthe plating bath 10 shown in FIG. 1. The jig conducts electric currentsupplied from the DC power source (plating power source) 14. When eachof the conducting pins 2-1, 2-2, 2-3, and 2-4 forms a reliableelectrical contact with the conductive film on the substrate 12, thenthe resistance between the pins is 0 or an extremely small value, andthe potential difference between the conducting pins will be 0 or anextremely small value. However, when one of the conducting pins is notin contact with or is in insufficient contact with the substrate 12,then this will create a large contact resistance that generates a greatpotential difference between this conductive pin and the others. Theelectrical resistance caused by this potential difference is measured bythe resistance measuring device 4-1 and 4-2.

Hence, when the resistance value measured by the resistance measuringdevice 4-1 is greater than a predetermined value, either the conductingpin 2-1 or 2-3 or both are not contacting or are forming a poor contactwith the substrate 12. When the resistance value measured by theresistance measuring device 4-2 is greater than a predetermined value,either the conducting pin 2-2 or 2-4 or both are not contacting or areforming a poor contact with the substrate 12.

FIG. 5 shows an example circuit configuration for implementing themethod for confirming conductivity between a semiconductor wafer and jigaccording to the present invention. The circuit in FIG. 5 differs fromthat of FIG. 4 as follows. The anode of reverse-current blocking diodes1-3 is connected to the connection point of the wire 3-1 and resistancemeasuring device 4-1. The anode of reverse-current blocking diodes 1-2is connected to the connection point of the wire 3-2 and resistancemeasuring device 4-2. The anode of reverse-current blocking diodes 1-4is connected to the connection point of the wire 3-3 and resistancemeasuring device 4-2. The anode of reverse-current blocking diodes 1-1is connected to the connection point of the wire 3-1 and resistancemeasuring device 4-1. The cathodes of the reverse-current blockingdiodes are connected as one to the negative electrode of the powersource 14.

With this construction, that is to provide reverse-current blockingdiodes 1-1 through 1-4, it is possible to prevent current fromcirculating between conducting pins and to measure electrical resistancebetween the same when there is only one conductive area between the jigand power source 14 of FIG. 1. Hence, when the resistance value measuredby the resistance measuring device 4-1 is greater than a predeterminedvalue, either the conducting pin 2-1 or 2-3 or both are not contactingor are forming a poor contact with the substrate 12. When the resistancevalue measured by the resistance measuring device 4-2 is greater than apredetermined value, either the conducting pin 2-2 or 2-4 or both arenot contacting or are forming a poor contact with the substrate 12.

FIG. 6 shows the general structure of a conductivity state sensor forthe plating apparatus according to a second embodiment of the presentinvention. A plurality of feeder contacts 15 contacts the conductivearea of the substrate 12, which is a semiconductor wafer or the like.Each of the feeder contacts 15 connects to a conductivity sensor 22. Thestructure of the plating apparatus according to the present invention isapproximately the same as that shown in FIG. 1, except the power source14 is connected between the anode 13 and the conductivity sensor 22.

During the operation for plating the substrate 12, the conductivitysensor 22 detects the conductivity state of each of the feeder contacts15. When poor conductivity (poor connection between one of the feedercontacts 15 and the conductive area on the substrate 12) is detected bythe conductivity sensor 22, thereby the conductivity sensor 22 opens aswitch 23 to turn off the power source 14 or issues a warning.

FIG. 7 shows an example construction of the conductivity sensor 22 in aplating apparatus according to the present invention. In the drawing,the conductivity sensor 22 includes a bridge circuit 24. The bridgecircuit 24 includes resistors 22-1 and 22-2 having predeterminedresistances R_(A) and R_(B), respectively; a current circuit 22-3 thatpasses through each of the feeder contacts 15, including contactresistances in the feeder contacts 15; and a variable resistor 22-4having a variable resistance R_(G). All of the resistors 22-1 and 22-2,the current circuit 22-3, and variable resistor 22-4 are connected inthe bridge circuit 24. A current sensor 22 a is connected in the centerof the bridge circuit 24. One bridge circuit 24 is provided for each ofthe feeder contacts 15.

In the conductivity sensor 22 described above, the resistance valueR_(X) of the current circuit 22-3 when the conductivity state of each ofthe feeder contacts 15 is normal is calculated by the followingexpression. Here, the resistance value R_(G) in the variable resistor22-4 is adjusted to achieve a detecting current of 0 in the currentsensor 22 a.

R_(X)=R_(B)/R_(A)·R_(G)

Since changes in the R_(X) of the current circuit 22-3 depend mainly oncontact resistance in the feeder contacts 15, a poor contact state inone of the feeder contacts 15 will increase the contact resistance,throwing off the balance of the bridge circuit 24. When the bridgecircuit 24 is unbalanced, a current will flow to the current sensor 22a. If the current exceeds a predetermined value indicating poorconductivity, a warning will be transmitted, or the plating power supplywill be shut off.

By incorporating the conductivity sensor 22 in the plating apparatus ofthe present invention, it is possible to detect the state of contactbetween each of the feeder contacts 15 and the conductive area on thesubstrate 12 prior to or during the plating process. As a result, it ispossible to prevent unevenness in the plating thickness caused by poorconnections by the feeder contacts 15.

In FIGS. 6 and 7, bridge circuits of current sensors 22 a are providedin the plating apparatus, one for each of the feeder contacts 15.However, it is also possible to provide only one bridge circuit 24 in acurrent sensor 22 a for confirming the conductivity (contact state) ofthe feeder contacts 15 by switching a switch. Further, while a bridgecircuit having a current sensor 22 a is employed in the examples above,the feeder contacts 15 can be directly connected to the current sensor22 a to directly detect current flowing through each of the feedercontacts 15, providing the current sensor 22 a has a high level ofsensitivity.

One method for sensing the state of conductivity between the feedercontacts 15 and the conductive area on the substrate 12 is to detect thecontact resistance by measuring resistance values between each of thefeeder contacts 15. As shown in FIG. 8, the resistance values betweenone feeder contact 15 and another is a combined resistance R0 of contactresistances R1 and R3 between the feeder contacts 15 and the conductivearea of the substrate 12 and resistance R2 of the conductive areaitself. Since the resistances R1 and R3 are approximately severalhundred mΩ, they must be measured with a high degree of accuracy.

FIG. 9 shows a fundamental circuit configuration for measuring thecombined resistance R0 with high degree of accuracy. As shown in thedrawing, the circuit includes an AC power source 31 (oscillatingcircuit), a constant current circuit 32, an amplifier 33, a synchronousdetection circuit 34 (multiplying circuit), and a low pass filter 35.The AC power source 31 outputs an AC voltage e₁ sin ωt to the X terminalof the synchronous detection circuit 34. The AC power source 31 alsoprovides a current to the constant current circuit 32. The AC voltagegenerated from the AC power source 31 passes through the constantcurrent circuit 32, which supplies a constant current to the combinedresistance R0. The voltage generated from both ends of the combinedresistance R0 is input into the amplifier 33. The amplifier 33 amplifiesthe signal and inputs the amplified AC voltage e₂ sin ωt into the Yterminal of the synchronous detection circuit 34.

The voltage output from the synchronous detection circuit 34 is obtainedby multiplying the AC voltage e₁ sin ωt with the e₂ sin ωt as follows.

(e1·e2·sin ωt²)/10={(e₁·e₂)/20}(1−cos 2ωt)

When this output voltage passes through the low pass filter 35, the lowpass filter 35 removes the cos 2ωt and outputs the direct current(e₁·e₂)/20. This DC output is proportional to the combined resistanceR0.

Since the combined resistance R0 is normally 700-900 mΩ, the resistanceof the wiring must be canceled in order to measure the combinedresistance R0 accurately. FIG. 10 is an equivalent circuit fordescribing a method of canceling resistance in the wiring. As shown inthe drawing, the equivalent circuit includes resistance values r1 and r2of wiring connecting the constant current circuit 32 to the feedercontacts 15 (A and B), and resistance values r3 and r4 of wiringconnecting the amplifier 33 to the feeder contacts 15 (A and B).Further, a current I_(M) flows from the constant current circuit 32; acurrent I_(V) flows to the amplifier 33; and a current I flows to thecombined resistance R0.

Since the amplifier 33 is an operation amplifier having a high inputimpedance of 100 MΩ, I_(V)<<I_(M) and I≈I_(M). Accordingly, sinceI_(V)≈0, the input voltage E_(M) of the amplifier 33 is as follows.

E_(M)=E−I_(v)(r3+r4)≈E

Here, E is the voltage on both ends of the combined resistanceR0=R1+R2+R3. The resistance R_(M) on the amplifier 33 side as viewedfrom the output side of the constant current circuit 32 is as follows.

R_(M)=E_(M)/I_(M)

R_(M)=E/I≈R0

It is possible to cancel r1-r4 of the above wiring resistance byconnecting the constant current circuit 32 and the amplifier 33 to bothends A and B of the combined resistance R0.

Next, a plating apparatus using the methods described above formeasuring resistance and canceling resistance in the wiring will bedescribed with reference to FIGS. 11-13. FIG. 11 shows the circuitconfiguration for measuring contact resistance at the feeder contactsand for supplying a plating current. FIG. 12 shows a circuitconfiguration of the contact resistance measuring device. FIG. 13 showsthe circuit configuration of the plating current supplying device. Asshown in FIG. 11, a terminal T₀ is connected to the anode 13; terminalsI₁-I₈ are directly connected to feeder contacts 15-1 through 15-8,respectively, on the jig 11; and terminals V₁-V₈ and T₁-T₈ are alsoconnected to the feeder contacts 15-1 through 15-8 via switches S₁-S₈.

As shown in FIG. 12, the contact resistance measuring device includesfour measuring circuits 41-1 through 41-4. Each of the measuringcircuits 41-1 through 41-4 has the same circuit configuration and willtherefore only be described for the measuring circuit 41-1. Themeasuring circuit 41-1 is provided with the AC power source 31, constantcurrent circuit 32, amplifier 33, synchronous detection circuit 34, andlow pass filter 35, as well as a DC amplifier 36 and an A/D converter37. The measuring circuit 41-1 also includes terminals V₁, V₂, I₁, andI₂ connected to terminals V₁, V₂, I₁, and I₂ in FIG. 11. The measuringcircuit 41-2 is provided with terminals V₃, V₄, I₃, and I₄ connected toterminals V₃, V₄, I₃, and I₄ in FIG. 11. The measuring circuit 41-3 isprovided with terminals V₅, V₆, I₅, and I₆ connected to terminals V₅,V₆, I₅, and I₆ in FIG. 11. The measuring circuit 41-4 is provided withterminals V₇, V₈, I₇, and I₈ connected to terminals V₇, V₈, I₇, and I₈in FIG. 11.

In the contact resistance measuring device described above, before theplating bath 10 (see FIG. 1) is filled with plating solution, theswitches S₁-S₈ are switched to the contact c side. The constant currentcircuit 32 in each of the measuring circuits 41-1 through 41-4 suppliesa constant current between each of the pair of feeder contacts 15-1through 15-8 on the jig 11, where the jig 11 is mounting a substrate(not shown). The voltage generated between each of the feeder contacts15 is measured via the amplifier 33, synchronous detection circuit 34,DC amplifier 36, and low pass filter 35. In this way, it is possible tocancel the resistances of the wiring to obtain a DC output proportionalto the combined resistance R0.

The DC output from the low pass filter 35 is converted to a digitalsignal by the A/D converter 37 and transferred to the CPU. The CPUdetermines whether sufficient contact is made by the feeder contacts 15based on this signal. If there is poor contact, the CPU reports whichfeeder contact 15 has insufficient contact. Poor contact can result fromnonconformity of the mechanical portion of the feeder contacts andsometimes can be corrected by retrying the problematic feeder contact15. If poor contact is detected, this retrying procedure is attempted.

If each of the feeder contacts 15 is attaining sufficient contactaccording to the contact resistance measuring device, that is, if allfeeder contacts are conducting properly, the switches S₁-S₈ are switchedto the contact a side. The plating bath 10 is filled with platingsolution, and the plating current supplying device as shown in FIG. 13supplies a plating current.

As shown in FIG. 13, the plating current supplying device includes eightplating current supply circuits 42-1 through 42-8.

Each of the plating current supply circuits 42-1 through 42-8 has thesame structure and is provided with a terminal T₀ and one of theterminals T₁-T₈. The terminals T₀ and T₁-T₈ are connected to terminalsT₀ and T₁-T₈ shown in FIG. 11.

Next, the structure of the plating current supply circuits 42-1 through42-8 will be described using the plating current supply circuit 42-1.The plating current supply circuit 42-1 is provided with a platingcurrent detecting circuit 38, a current control circuit 39, and a powersource 40. The current control circuit 39 sets the circuit value basedon a command from the CPU for plating conditions. A plating current ofthe value set by the current control circuit 39 is supplied from thepower source 40 through the terminal T₀, anode 13, substrate 12 (seeFIG. 1), each of the feeder contacts 15-1 through 15-8 on the jig 11,each of the switches S₁-S₈, and each of the terminals T₁-T₈.

The plating current detecting circuit 38 detects plating current flowingthrough each of the feeder contacts 15-1 through 15-8 and outputs adetection value to the current control circuit 39. The current controlcircuit 39 controls the power source 40 to provide a plating currentwith the value set above. Hence, if the current flowing through each ofthe feeder contacts 15-1 through 15-8 is set at a uniform value, it ispossible to supply a uniform plating current through each of the feedercontacts 15 to form a uniform plating thickness on the substrate 12.

While example constructions of a contact resistance measuring device andplating current supplying device described have been described indetail, the concept of the present invention is not limited to thosedescribed above.

In the embodiments described above, a conductivity sensor is provided todetect the conductivity of a plurality of feeder contacts. Accordingly,it is possible to confirm the conductivity at each feeder contact,thereby eliminating one cause of non-uniformity in plating filmthickness.

Further, a plating current detecting circuit is provided to detect thecurrent flowing through each of the feeder contacts, and a currentcontrol circuit is provided to maintain the plating current at a uniformvalue based on the value of the current flowing through the feedercontacts detected by the plating current detecting circuit. Accordingly,it is possible to supply a uniform plating current through each of thefeeder contacts to form a plating film on the plating surface of thesubstrate at a uniform thickness.

Industrial Applicability

The plating apparatus of the present invention can be used in the fieldof semiconductor fabrication and the like, as the invention enables theformation of a uniform plating film on a substrate, such as asemiconductor wafer and the like.

What is claimed is:
 1. A plating apparatus for plating a substrate,comprising: a plating bath; an electrode disposed in the plating bath; asubstrate mounted opposite the electrode and having a conductive area onits surface; a plating jig disposed in the plating bath for retainingthe substrate and having a plurality of feeder contacts for contactingthe conductive area on the surface of the substrate; a voltage supplyingdevice for applying a voltage to supply a predetermined current betweenthe plurality of feeder contacts and the electrode, thereby generating acurrent flowing for plating the substrate through the feeder contacts;wherein, the feeder contacts of the plating jig are electricallyseparated from each other; and for each feeder contact, one end of areverse-current blocking diode is connected to wiring connecting thefeeder contact, and the other end of the reverse-current blocking diodeis connected to wiring connecting said voltage supplying device; and aconductivity state detecting device is provided for detecting theconductivity between each of the feeder contacts on the plating jig andthe conductive area on the surface of the substrate.
 2. A platingapparatus according to claim 1, wherein the conductivity state detectingdevice comprises a contact resistance measuring device for measuringcontact resistance between the feeder contacts and the conductive areaon the surface of the substrate, and is adapted to detect theconductivity state of the feeder contacts based on the contactresistance measured by the contact resistance measuring device.
 3. Aplating apparatus according to claim 2, wherein the contact resistancemeasuring device comprises an alternating current oscillating circuit, aconstant current circuit, a synchronous detection circuit, and a lowpass filter; whereby the alternating current oscillating circuitsupplies an alternating current between the feeder contacts via theconstant current circuit, and the AC voltage generated between thefeeder contacts is input into one of the input terminals on thesynchronous detection circuit, while the AC voltage of the alternatingcurrent oscillating circuit is input into the other input terminal ofthe synchronous detection circuit, which multiplies the two AC voltages,outputting the result through the low pass filter to obtain a directcurrent output proportional to resistance value between the feedercontacts.
 4. A plating apparatus according to claim 2, wherein thecontact resistance measuring device further comprises a canceling devicefor canceling the resistance in wiring used to connect the contactresistance measuring device between the feeder contacts and which isadapted to eliminate the influence of resistance in wiring on themeasurement results.
 5. A plating apparatus according to claim 2,wherein a plating current detecting device is provided for detecting aplating current flowing through the feeder contacts, and a platingcurrent controlling device is provided for maintaining a uniform platingcurrent flowing through the feeder contacts based on output from theplating current detecting device.